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Programable Themostat Connections

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Joined: Apr 11 2003

We just purchased a programable thermostat and the wire connections for the unit do not match those that went into the original manual Honeywell thermostat. The connections on the back of the original unit are labeled "L1" and "T1" and the connections on the back of our new Ritetemp programable unit give the choices of "C", "RC", "O", "B", "RH", "W", "Y", & "G".

The installation directions for a "2 - Wire" installation which I assume I must have because I only have 2 wires emerging from the wall indicate connecting to the "RH" and "W" terminals but which of those correspond to the designations of "L1" and "T1" on my original thermostat?

Any help would be greatly appreciated.


Joined: Mar 21 2003

Be careful!

Our house (and I believe other Eichlers with the original boilers) uses a 110v AC thermostat. Most of the Home Depot/aftermarket programable thermostats are low voltage. Hooking them into a 110v control circuit would be a bad thing to do. At the least the new thermostat would be destroyed, at worst sparks, flame and smoke. . .

So get check your thermostat control circuit with a volt-ohm meter before proceeding.

Joined: Jul 1 2003

We have a 1973 Eichler and I recently replaced a Honywell manual mercury (not sure if it was original, but it looked like it).
Per the previously posting, you have to determine whether the thermostat is "24V" or "Line Voltage 120V"; 24V is common while 120V is rare, but Tod said he has a 120V control system.
Unless your RiteTemp specifically said Line Voltage, it's should be a 24V unit. Normally, you need to turn off the electrical to the Furnance, but if you follow Tod's advice and use a voltmeter, you need to have the juice stay on (and DON'T short the 2 wires). I took the chance that my system is 24V without checking - - I also had a humming sound around the Furnance from the 24V transformer (but Tod's 120V setup would have made me re-think what the humming sound is; it also could be the door bell transformer which is also low voltage). In any event, the odds are you have a 24V sytem but "You pays your money and takes your chances."
Next, you asked about the 2 wires - - my old Honeywell had (I think) "R" (red) and "W" (white) labels with corresponding colored wires -- can you assign the color wires to the L1 and T1 connections?? If your setup is similar to mine, the odds are the Red wire should be connected to RH on the RiteTemp (I'm not at home, but the wire should be red but could be black); the other wire, should be white and connected to the W connector - - I'll check the colors on my setup and write again -- - the other connectors control combined heating & A/C systems with a central fan which Eichlers don't have. The RiteTemp should also have a jumper wire to the RH connector from another connector (leave it in place in case it is needed by the RiteTemp).
A comment about a programmable thermostat -- there are postings about how many degrees to "set back" - - in my location in Sunnyvale, the BR's face west and are cooked in the afternoon until sunset; then the outside air cools the BR area after midnight. The problem with radiant heat is that it's slow to heat - - thus, the advice from radiant heat people is to not set back more than 3-4 degrees because it can take hours to heat the house to your comfort setting if the house is allowed to cool down too much. However, the warm daytime weather in No. CA. doesn't result in extreme daytime temperature drops in the house - - thus, I found the primary benefit of a programmable thermostat is to turn off the furnance when everyone is awake (say by 7:30am) and activate your sleeping comfort setting (say 11pm when outside air cools down the house) - - before, I would manually turn off in the morning and re-set at night. Depending on the features of the RiteTemp, you may have a capability to monitor the hours your furnance is running - - I don't have the feature in my Lux unit but do have a filter monitoring feature which I use to monitor how long the furnance is operating. Another feature the RiteTemp probably has is the "swing" setting - - you set it to 1, 2, 3 or more degrees where the system doesn't respond until the temperature change EQUALS or EXCEEDS the swing; thus, if you set your comfort level to 75d and a swing of 2d, the thermostat will activate the furnance at 73 and heat until 75, which can take several hours.
A 3rd thing to note is the hallway placement of the thermostat; we have a courtyard model so the hallway is surrounded by rooms so it tends to be hotter than the rooms which form the exterior; thus, I have higher readings than if the house is an atrium model where the hallway has considerable exposure to exterior glass or exterior walls. For the first week, I literally got up at 2-3am to assess whether it was warm enough - - it wasn't, so I increased the comfort setting to the next lowest level (which was 76) to activate the furnace so our daughter's BR would get warmer; I then ignored the typical recommended settings of 68, 70, 72 etc. because the hallway never go that low.
Our radiant system is somewhat uneven in heating; our master BR is typically warm but our daughter's BR typically runs a bit cooler; I don't know whether we can adjust (I'm still looking for the mysterious manifold to do this) or whether it's the floor covering (the MBR is tile while the other BR's are Pergo laminate). In any event, the programmable thermostat doesn't solve this problem.

Joined: Jul 1 2003

Jay: I realize I was rambling in my posting. Here's the condensed version:
(1) Try to determine whether you have a 24V or 120V system. As I said, I took the chance it was 24V without a lot of clarity. If it was 120V, I think the old Honeywell thermostat would have warnings about using it only for line voltage 120V systems.
(2) If you feel safe to proceed, turn off the electrical to the furnance at the circuit breaker panel. I confirmed electric was off by trying to activate the furance before removing the old thermostat.
(3) Before unscrewing the 2 wires, I confirmed that the wires were connected by color - - i.e., red wire to R, and white to W. In your case, you say the markings are L1 and T1, so the markings are no help.
(4) Install the RiteTemp back panel and connect the red wire to RH and white wire to W. The RiteTemp requires batteries, so have fresh akalines before your start the entire installation. The batteries will power up the thermostat.
(5) Turn on the power at the breaker panel and if the RiteTemp remains powered , then you're safe, and before spending more time on it, set the unit to heat (I assume your unit is multi-purpose w/ A/C and fan). Then set the comfort temperature low to activate the furnance, and if the furnance comes on, your installation is perfect. Now, you just need to set the comfort temperatures for each period of the day/night and other features (like the clock, etc.).

Joined: Apr 5 2003

The key giveaway whether the thermostat is 120 volts or 24 volts will probably be the size of the wires. On our 120 volt system, the electricity comes from the breaker panel, goes through the thermostat (which switches the 120v on and off as the temperature goes up and down), then goes off to the boiler. Because the thermostat needs to control high power and voltage, the thermostat will connect with the same sort of wires that light switches and outlets have -- thick copper wires either wrapped in cloth or thick plastic, and sometimes leading into a bundle with other wires, and typically covered black and white. (If you go looking in the wire department at Orchard, compare your wires to the 12 or 14 gauge wire.)

With the 24 volt system, the power goes from the panel to the furnace; there's usually a switch so the furnace guy can shut off power, but normally the boiler always has power. The boiler gets controlled by two small wires that run to the thermostat. These wires are the same thickness as those in your doorbell or that you'd use for model trains. These wires are usually 18-20 gauge, red and white.

If the wires leading to the thermostat are the size of thin spaghetti and can easily be bent with a couple fingers, they're probably 24 volt. If the wires leading to the thermostat are much thicker, they're probably 120 volt.

Remember that your mileage may vary. Previous owners could have done some very sick things when doing repairs on the house. For better safety, get a little 120v circuit tester. (My favorite is the small screwdriver with a neon bulb in the handle; when you touch the top of the handle with your finger and touch the blade to an electrical wire, the light will glow if the wire is the "hot" side of the electrical circuit.) If the light glows when you touch terminals on the current thermostat, then it's 120 volt.

Hope this helps.


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